Omega-3 fatty acids are long-chain polyunsaturated fatty acids synthesized by marine microalgae and accumulated in the form of lipids by higher marine organisms such as fish. Since Dyerberg and Bang (Acta Med Scand, (1976) 200:69-73) established the relationship between dietary marine fish consumption and reduced incidence of coronary heart disease, numerous studies have confirmed several specific effects of a diet high in polyunsaturated fatty acids. Among these are the reduction of triglyceride levels in blood (Sanders, T. A. B. et al., Arteriosclerosis, (1985) 5:880-5), and reduction of low density and very low density lipoproteins (Illinworth, D. R. et al., Arteriosclerosis, (1984) 4:270-5). Furthermore, cancer studies show that omega-3 fatty acids may help to decrease the incidence, growth, and metastatic spread of tumors Karmali R. A. et al., JNCI, (1984) 73:457-461.
Since it has been shown that the consumption of omega-3 fatty acids from fish has a beneficial effect in reducing the incidence of coronary heart disease, alternative sources of omega-3 fatty acids have been sought to provide these benefits where consuming large amounts of fish is not desirable or practical. One of these sources is marine microalgae, which produce significant quantities of omega-3 fatty acid. It has been reported that some species of marine microalgae have an omega-3 fatty acids content ten fold higher than fish oils on a dry weight basis. Kyle, D. et al., World Conference on Biotechnology for the Fats and Oils Industry, (1988) p. 117-22.
Another method for providing higher levels of omega-3 fatty acids without consuming large amounts of fish oils is upgrading. There are several methods for upgrading fish oils which result in their enrichment with omega-3 fatty acids. For example, oils which have a high content of saturated fatty acids can be "winterized" by slow cooling to about 5.degree. C. The major drawback of "winterization" is insignificant enrichment (about 10%) of omega-3 fatty acids.
Another technique is molecular distillation. The process takes place at high temperatures and low vacuum (of the order of 10.sup.-6 mm Hg). This process is highly energy consuming and results in a significant distraction of labile highly unsaturated fatty acids.
Other methods, which require the use of organic solvents, include crystallization, chromatography and supercritical carbon dioxide extraction. These processes have a number of drawbacks. For example, crystallization typically results in only small omega-3 enrichment of the product, and chromatography and supercritical fluid extraction are expensive and difficult to scale up.
Another approach for concentration of omega-3 fatty acids is based on chemical hydrolysis (or esterification) of fish oils, which is followed by a complex purification.
An alternative approach for enrichment of omega-3 fatty acids is based on lipase-catalyzed enzymatic refinement of fish oils. For example, Japanese patent 134446, June 29, 1984, to Kao Corp., describes a process which utilizes a lipase, Arthrobacter urefaciens, which is specific for saturated fatty acids, for the hydrolysis of fish oils. A similar process which is based on the natural preference of some lipases for saturated fatty acid moieties is described in Japanese patent 134446, Jul. 16, 1982, to Nippon Oils and Fats Co.
A different approach, which results in the production of triglycerides enriched in omega-3 fatty acids, is based on a two step enzymatic process. Japan Patent 234,588, Nov. 21, 1985, to Asahi Denka Kogyo Co.
There are several limitations to the enzymatic processes described above. These include the necessity for a complex separation of the product from free saturated fatty acids, which are the by-products of the hydrolysis reaction, and use of complex multienzymic systems and low efficiency that results in an insufficient degree of upgrading. An efficient cost-effective method of enriching the level of omega-3 fatty acids is needed.